Seedling in the Rhynie chert – a
less-common sight
Germinating spores and subsequent growth stages up to adult
gametophytes* have been documented for the most abundant plants in the
Rhynie chert, Aglaophyton
and Rhynia
[1,2]. (One related publication
involves a misinterpretation, see Rhynie
Chert News 8.
) Still obscure are the early
stages of the sporophyte generations. This makes any one of the rarely
seen early stages of plant growth an object of special interest.
Figure: Early growth stage of a Rhynie chert plant, height
0.8mm,
with rhizoids.
Note the orientation of the cells on the left,
possibly
indicating the onset of sideward growth.
Sub-millimeter-size blobs with cellular structure are occasionally seen
in the chert. If they bear rhizoids, as in the present case, they can
be identified as early stages of growth. Lucky incidences providing
optimal cuts are obviously rare, and in fact this one is the only own
find of this kind. The tiny baby plant with rhizoids seen here was
unexpectedly found in a big chert sample with abundant Aglaophyton and
a few Rhynia.
The orientation of the cells on the left seems to indicate a beginning
sideward growth. Hence the object could possibly be an early stage
(protocorm) of
the Rhynia
gametophyte (named Remyophyton)
whose variable shape and
sideward growth is pictured in [2].
The present find can serve as an encouragement to look for more tiny
objects possibly representing early stages of either gametophyte or
sporophyte of any Rhynie chert plants whose adult stages are well known.
* Annotation: The life cycle of the Rhynie chert plants
involves
alternating generations of short-lived smaller gametophytes and sturdy
sporophytes, similar as with extant ferns. The gametophytes of the
Rhynie chert plants, which come in male and female versions, produce
sperm and egg cells, respectively. The sporophyte, which is the
"proper" plant, grows from a fertilized egg cell, probably while
the
gametophyte wilts and decays. Gametophytes are seldom seen in the
chert, probably
because of their short life and fast decay. Gametophytes have been
given names different from the related sporophytes.
H.-J. Weiss
(2008)
[1] W.
Remy, R. Remy:
Lyonophyton rhyniensis …,
Argumenta Palaeobotanica (Münster)
6(1980), 37-72, Tafel 7-13,.
[2] H.
Kerp, N.H. Trewin, H. Hass: New gametophytes from the
Early Devonian Rhynie chert,
Trans. Roy. Soc. Edinburgh, Earth
Sciences 94(2004 for 2003), 411-28.
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